1. Field of the Invention
This invention addresses injuries and disorders of the musculoskeletal system in general and finger joints in particular, and relates to medical and surgical methods and devices for the correction of these conditions. More particularly this invention provides dynamic orthopedic methods and devices that increase the range of motion of finger joints suffering from contractures.
2. Description of the Prior Art
Skeletal joint contractures (also known as flexion contractures), including fractures and dislocations of joints which reduce the range of motion of the joints, may result from trauma or from bums and the scars left after bums heal. Contractures also result from muscle imbalance across joints and often accompany diseases such as leprosy and Dupuytren""s disease. Dupuytren""s disease, for example, commonly causes flexion contractures of the small joints of the hand. Any skeletal joint may be subject to disorders or abnormalities of this nature.
Conditions such as these have traditionally been treated by a variety of modalities including splinting, serial plaster casts, and surgical release. Recently, significant innovations have resulted in more effective dynamic methods of treating such injuries in certain joints. One of these innovations is a dynamic finger joint support with a continuous passive motion machine that applies torque to the proximal interphalangeal (PIP) joint to flex and extend the joint. This device is disclosed in U.S. Pat. No. 5,376,091 to Hotchkiss et al., entitled xe2x80x9cDynamic Finger Support,xe2x80x9d issued Dec. 27, 1994, and incorporated herein by reference. Another innovation is that of Messina et al., as described in Messina, A., et al., xe2x80x9cThe TEC treatment (continuous extension technique) for severe Dupuytren""s contracture of the fingers,xe2x80x9d Annals of the Hand and Upper Limb Surgery 10(3); 247-250 (1991); Messina, A., et al., xe2x80x9cThe Continuous Elongation Treatment by the TEC Device for Severe Dupuytren""s Contracture of the Fingers,xe2x80x9d Plastic and Reconstructive Surgery 92(1): 84-90 (1992); and Citron, N., et al., xe2x80x9cThe use of skeletal traction in the treatment of severe primary Dupuytren""s disease,xe2x80x9d The Journal of Bone and Joint surgery 80-B(1): 126-129 (1998).
A disadvantage of some prior art devices is that the torque that these devices impose to increase the range of motion of the joint is applied through the skin overlying the skeletal segments extending from one or both sides of the joint. An aggravating factor is that the torque must be applied for a significant amount of time before it will successfully increase the range of motion of the joint. If the torque is transmitted to the skeleton indirectly through the skin, the force applied to the skin compromises circulation under the contact site and causes the skin to become tender, red and inflamed. In severe cases, particularly those with compromised sensation, ulcers may develop. For the distal interphalangeal (DIP) joint (the outermost knuckle of the finger) and the proximal interphalangeal (PIP) joint (the middle joint of the finger), the Hotchkiss et al. device avoids this problem by applying force directly to the phalanges that are proximal and distal to the joint being treated, the force being applied through pins embedded in the phalanges themselves through the lateral (side) surfaces of the phalanges. The Messina et al. device similarly applies force through pins embedded laterally in the phalanges distal to the joint being treated and in the hard bones proximal to the joint.
While the Hotchkiss et al. device, the Messina et al. device, and similar devices have achieved success, these devices have certain limitations. Because of the laterally extending pins on these devices and the external elements attached to these pins, these devices are difficult to use on the middle and ring fingers and are instead more useful for joints on the border (index and little) fingers. In addition, the lateral and medial surfaces of the phalanges, particularly those of the proximal phalanges of the fingers, are covered with tendons and other soft tissues that may be punctured when pins are inserted in the sides of these phalanges as Hotchkiss- and Messina-type devices require. A further difficulty is that installation of these devices on the PIP joints of the long or ring fingers necessitates partial spreading of the adjacent fingers, and the spread position must be maintained throughout the treatment period. In general, a Hotchkiss- or Messina-type device on one finger tends to interfere with the use and movement of adjacent fingers and the use of the hand, especially the palmar surface of the hand, for pinching and grasping.
Of potential additional relevance to this invention is U.S. Pat. No. 6,063,087, to Agee et al., entitled xe2x80x9cMethod and Apparatus for Increasing the Range of Motion of Fingers Suffering From a Limited Range of Motion, Through an External Force Transmitted to the Skeleton,xe2x80x9d issued May 16, 2000. This patent discloses a device that avoids the use of laterally oriented pins for securement to the proximal and/or middle phalanges, utilizing instead pins that are securable to the dorsal surfaces of the phalanges, especially the dorsal surface of the middle phalanx. Like the Hotchkiss-type devices, the device of U.S. Pat. No. 6,063,087 applies a torque to the PIP joint by way of a torque axis that passes through the joint itself.
Features that would be particularly beneficial in a device for treating contractures of the PIP joint include the following:
(a) the ability to apply a controlled torque to the interphalangeal joint being treated, i.e., a torque that does not deviate widely from a central value as the joint pivots through its full range of motion,
(b) the ability to impose a torque on the PIP joint without imposing a significant torque on any other joint including those associated with the same finger, and in general:
(c) a simple construction that combines torque and a wide range of motion to the subject joint throughout the angular range of the joint while maintaining a secure attachment of the device to the patient,
(d) ease of manufacture, and
(e) adaptability of use for skeletal differences among individual patients.
The limitations and goals set forth above and others are addressed by the present invention, which resides in a device for treatment of a finger suffering from a disorder involving a limited range of motion of the proximal interphalangeal (PIP) joint of a finger, specifically a contracture of the joint, or for the treatment of such disorders of two or more fingers on the same hand. For the particular finger requiring treatment, the device includes two pivotally joined sections, means for securing the two sections to the patient, and a torque-producing element that produces a torque about the pivot point in a direction that urges the sections toward the parallel. The various components are arranged such that the pivot axis about which the two sections rotate is dorsal to the finger and the torque-producing element and the pivot axis define a moment arm that either remains substantially constant while the torque produced by the torque-producing element varies or decreases as the torque increases. As a result, the device applies a predictable and controllable level of torque to the finger joint throughout the angular range of motion of both the device and the finger joint.
The terms xe2x80x9ctorque-producing elementxe2x80x9d and xe2x80x9ctorque-producing memberxe2x80x9d are used herein to denote any element that, either by itself or in conjunction with the pivot point, imposes a torque on the PIP joint, The terms therefore encompass elements such as elastic bands or linear springs that are stretched between two points on the device each located at a distance from the pivot point such that by imposing tension between the two sites the band or spring imposes a torque about the pivot point, as well as elements that engage the pivot point itself and create a torque directly.
One of the discoveries arising from this invention is that despite the shift of the pivot axis to a location away from the joint itself, an effective and controllable torque can be applied to the PIP joint as the joint rotates. Another discovery is that when the pivot axis and the torque-producing element are positioned such that the length of the moment arm varies in inverse relation to the force applied to the torque-producing element (i.e., the moment arm lengthens as the torque-producing element is relaxed), the relative positions of the pivot axis and torque-producing element can be adjusted to produce a torque that remains relatively steady as the joint flexes. A further discovery and advantage of the invention are the ability of the device to impose a torque on the PIP joint without imposing a functionally significant torque on any of the neighboring joints, including the metacarpal phalangeal (MP) joint on the same finger. Still further discoveries and advantages will be apparent from the description that follows.